Engineering drawings are relatively large documents which may have widths of as much as 84 centimeters, or 33 inches and lengths as much as 119 centimeters or 47 inches. In prior art electrophotocopying machines, an image of the original is focused by a lens, usually of the reflex type, upon a photoconductive drum. In order to expose a relatively large document such as an engineering drawing within a reasonable time such as approximately seven seconds, it is found that the power input to a tungsten halogen illumination lamp is approximately 46f.sup.2 watts, depending upon the f number of the lens assuming a magnification of unity. A standard 110 volt outlet has a maximum current rating of 15 amperes which provides a power output of 1650 watts. The smallest lens which can be used would be f-6. Such lens would have a diameter of approximately 19 centimeters or 7.5 inches and weigh approximately 11 kilograms or 24 pounds. It is clear that the cost of such large lenses would be inordinately high.
In making copies of engineering drawings, diazo machines are usually employed using coated papers, where the exposure is by contact rather than by the focusing of an optical image. While contact exposure has a relatively high efficiency, it has not been considered suitable for electrophotographic copiers, since contact between the original document and the photoconductive drum would result in the deposition of some toner upon the original document and would also moisten the original document where liquid developers are used. Since engineering drawings may be large documents upon which many man hours have been spent, it is absolutely essential that they not be damaged by the electrophotocopier. For unity magnification contact exposure, the power required by a fluorescent lamp to expose a relatively large engineering drawing in seven seconds is approximately 0.18/D watts, depending upon the transmittance D of the original. Even if the transmittance of the original is as low as 0.24%, the fluorescent lamp power required is only 75 watts. Since very high output fluorescent lamps can operate at 0.9 watt per centimeter, an 84 centimeter fluorescent lamp can be used.